class Client extends Page { 

   static $db = array(
   );

   static $has_one = array(
     'myOffice' => 'Office'
   );

   function getCMSFields() {
      $fields = parent::getCMSFields();

      $oData = (DataObject::get('Office'));
   	if ($oData) $OfficesSource = $oData->toDropDownMap('ID','Title');   	
	$fields->addFieldToTab('Root.Content.Main', new DropdownField(
			'myOffice',
 		  	'Office',
 		  	$OfficesSource,
 		  	$this
		),
		'Content'
	);
   return $fields;
}

class Office extends Page {
   static $db = array(
   );
	
   static $has_many = array(
    	'Auditors' => 'Auditor'
   );
}